Dominos' Effect
by HikarinRin
Summary: [ONESHOT] Sequel from Instinct, Alpha/Beta/Omega Dynamics, Heat, Incest, Knotting, Self-Lubricant, Alpha!Kara, Omega!Todo, Dirty talking.


Dominos' Effect

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Disclaimer : Osomatsu-san is not mine.

Pairing : Karamatsu Todomatsu

Genre : Alpha/Beta/Omega Dynamics, Smut, Knotting, Self-Lubricating, Romance, Lemon, Mature.

Warning : Many dirty talking, definetely porn, not for kids, and please back up if knotting and wolfau thingy is not your cup of tea.

Rating : R18, _**Continue at your own risk!**_

Words count : 2,7k

By : Hikari Rin

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After a long week of Choromatsu's heat, everything finally calmed down. Osomatsu finally stopped growling at everyone一 _even those who tried to put food in front of their door一,_ and Choromatsu's pheromones finally stopped blasting.

It's really tempting for Jyushimatsu and Karamatsu as an Alphas. No one can resist the animalistic urges to knot and ground an Omega's first heat.

But, as a sextuplet, something as _Dominos' Effect_ is not impossible, right?

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It's a new bright morning when Karamatsu, Todomatsu, Jyushimatsu, and Ichimatsu wake up by Osomatsu's loud door's screeching.

"Yo, brothers.", he said sleepily as he yawns and scratch his stomach.

Karamatsu is the first one to wake up and then rubs his eyes as he looks at his older brother.

"Ah, brother! How is it? Is it fun? Oh my, you got many aggressive bite marks, aren't you?", he chuckles as he caress Todomatsu's hair that's on his lap.

"Ah, yeah. It's his first and he triggered my rut, so if you put two and two in one, you can get something like this", he said lazily as he opened the fridge.

"Well, that's kind of unfortunate yet fortunate. Where is Choromatsu?", Karamatsu looks at the door and wondering why Choromatsu is not with his older brother.

"Ah, come on. You know what Omegas needs after their long mating.", Osomatsu replied with a mischevious smirk plastered on his face.

"Oh, right. I forgot. Sorry for my stupidness, brother! I don't know how to apologize properly because of my stu一omph!"

Karamatsu's setence immediately being cut by a slipper thrown on his face.

"Ittai, ittai, ittai! Stop that, Karamatsu! You're ruining my morning! Anyway, i'll heads up to Choromatsu, okay? Just in case he'll cry if his Alpha is not there for him", Osomatsu winked and then laughs as he went upstair.

Karamatsu rubs his nose and then stretch his body, But then, something sweet like rose and honeyscukle going into his nostrils and his instinct perked up in awareness.

 _What is it? This is the smell of an Omega's heat. But who? Choromatsu's already done._ , Karamatsu said in his thought.

And then he hears soft whimpers coming from someone under him.

 _'Todomatsu?'_ , Karamatsu rises his eyebrows.

Todomatsu slowly flutters his eyes open and his face slowly becoming red as fat sweats rolling down from his temple.

He tried to get up but his hands and his legs feel so weak and all he can do is just whimpering as he looks at Karamatsu pleadingly.

"Ka..Karamatsunii-san...", Todomatsu moans softly as he reach out for his Nii-san's jacket weakly.

Karamatsu's eyes are widen up and he panickly looks around and found Jyushimatsu's starting to squirm.

 _'Oh no, his Alpha instinct is strong. He must've sensed Todomatsu's heat!'_

Karamatsu hurriedly wakes Jyushimatsu and Ichimatsu up. He told Ichimatsu that Todomatsu's heat is coming suddenly and he must take Jyushimatsu away.

Ichimatsu of course understand the urgency and without saying anything, he drags Jyushimatsu away before he fully awake.

"Nii-san... It's hot... Nhh..", Todomatsu softly whimpers again as his breath coming out in staccato.

Karamatsu immediately locks the living room and pulling out a spare futon. Yes, they have futon here just in case someone heat is unpredictable come.

"Yes, Todomatsu. It's okay, i'm here", he said softlt as he slowly pick his little brother up and put him down on the mattress.

Oh, how bad he wants to release his beast inside. I mean, look at how miserable Todomatsu now. Obvious bulge, his slick already running down to his thigh, and his moans are getting needy. But of course, as a good Alpha, he doesn't want to hurt his Omega.

He softly but quickly takes off his own shirt and his pants, leaving him clad only in his boxer.

"Nii-san.. Hhah.. P-please...", Todomatsu whimpers and his hands starting to palm his own erection from outside.

It's painful, how his growing erection straining against his jeans. And as soon as Karamatsu took off his shirt, his Alpha scent is going straight into Todomatsu's nostrils and oh how he wants to sniff that more.

Karamatsu chuckles and helping his little brother to take off his shirt and taking off his jeans. But as soon as the last thing coming off, a strong sweet and delicious scent blasting off and Karamatsu almost growls loudly.

He shakes his head and trying to clear his mind and taking off Todomatsu's last garment off his body.

"Nii-san.. Please.. Please.. Fill me..", Todomatsu moans needily as he automatically turning around to all four and press his chest down, giving a signal as his submissiveness finally taking over.

Karamatsu's breath hitched as he saw his Omega submitting. The view is really mouth-watering for the Alpha.

Inviting pink hole that served right in front of his face, coming side by side with the slick that's dripping out more and more to the thighs, and needy whimpers that slowly becoming louder.

Karamatsu gulps and trying to hold onto his last sanity. Of course his dick finally fully erected and it's straining against his boxer.

"Todomatsu.. Please let me prepare you, okay? That's the only thing that i can do before my Alpha ravishing you.", Karamatsu said lovingly as he caress Todomatsu's back, going down and down until his palm rested above Todomatsu's entrance.

"Y-Yes.. B-But.. Please.. H-Hurry...", Todomatsu bites his lips as his dick twitched in anticipation.

Karamatsu suck his index and middle finger, and then slowly inserting both fingers in one go.

"Fuck, Todomatsu.. It's always tight like the first time. Omegas sure are incredible, huh?", Karamatsu licks his dry lips as he continue to finger the writhing Omega.

"A-ah! Ngh! Y-Yes..! Y-Yes! P-Please more, Nii-san...", Todomatsu moans lewdly as he moves his hips back to insert Karamatsu's fingers deeper.

Karamatsu gulps as his mind start to wander. He loves the way the Omega's walls clenching around his fingers when he curl his finger to rub his prostate. He loves the way Todomatsu screams more and letting out a chain of "Ah"'s as his mind starting to get lost and lost in pleasure.

Todomatsu needs more. He needs more. He needs the knot. He needs something larger and bigger to split him into two. So he said it.

"Please..", he whimpers softly.

"Hm?"

" _Alpha.._ "

And then Karamatsu lose it. His Omega is calling him and the last self-restraint that he have is jumping out from the window.

Karamatsu pulls out his fingers and takes off his boxer. He climbs on top of Todomatsu and bends down.

"Fuck, you're having fun in playing with my inner Alpha, aren't you, _Omega?_ ", He whisper deeply at Todomatsu's ear.

His words replied by a loud moans from his Omega underneath him. "Ng-Ah! Y-Yes! P-Please, hurry!", Todomatsu screams in frustration.

Karamatsu's eyes starting to glowing bright red and he growls dangerously, sending Todomatsu to lowers his needy whimpers and lowering his head in submissiveness.

"Did you just ordering around your Alpha?", Karamatsu asked.

"N-no, Alpha..", Todomatsu whimpers. He liked this side of his Nii-san, the dangerous and strong Alpha.

"Then? Do you know your place? How should you talk to your Alpha?"

"... B-Beg.."

"Good boy. Now what, Omega?", Karamatsu whisper even deeply, sending shivers down to Todomatsu's spine and making his slick trickle even more.

Karamatsu teasingly rub his dick's head against Todomatsu's puckering hole that's twitching in hunger to be filled.

"P-Please Alpha...", Todomatsu whimpers as he can't take it anymore teasing. His stomach hurt and his heat is getting stronger. His head is spinning and he wanted to cry because all of it.

"Please what?"

".. Please, k-knot me. Pound me into oblivion. Thrust it deeply into me and fill me with your pups!", Todomatsu whimpers loudly and he start to push his hips backward, needing his Alpha's dick so bad.

"Good boy.", Karamatsu said and he slowly pushing in his length inch by inch.

Todomatsu start to trembles in pleasure and every inch of his Alpha's dick pushing out more and more moans from his throat.

He loves it so much. The burning pain of being stretched so wide yet the pleasure of being filled by his Alpha is coming hand in hand.

He moans loudly as Karamatsu finally settles deep inside him until the hilt. It's so good, being filled so full like this.

"Do you like it, Omega? When i grind you like this?", Karamatsu start to grind his hips and it tore lewd moans from Todomatsu.

"Ah! Y-Yes! I-I love it!", Todomatsu screech as his walls clamping down on Karamatsu's length.

"Such a dirty, Omega.", Karamatsu chuckles and he start to pull back , leaving the tip of his length before pushing in again.

He start with shallow thrusts, still making sure that he hears no more painful whimpers coming out from his Omega's mouth.

"A-Ah... Hhah.. H-harder... Alpha...", Todomatsu moans loudly as he push his hips back to meet his Alpha's thrust halfway.

Karamatsu licks his lips and he grab Todomatsu's hips, holding him in place before he start to pound into Todomatsu hardly.

"Ah! A-ah! G-Good! I-It feels so good, Nii-san..!", Todomatsu screams in pleasure as he grabs the sheet hardly. Tears starting to pool in the corner of his eyes and slowly falling down to the mattress.

"Do you like it, Todomatsu? Hhah.. When i pound you so hard like this? Your walls are clencing around me so bad", Karamatsu groans and his breath getting harder.

It feels so good for him. His Omega's walls are squeezing him and the nasty squelching sound everytime he pulls out and pushing back in. Todomatsu's moans and screams when he hit his spot dead on are a pure melody for him to get faster and faster.

"Y-Yes! A-Ah! I-I want to cum, Karamatsunii-san! Ah! Ah!", Todomatsu moans even louder, doesn't even care if people outside hearing his dirty and needy whimpers.

"You want to cum, baby? But you're not allowed to cum if i say no, okay?", Karamatsu chuckles and he stop for a while, shifting his hips before starting to thrust hardly again.

"A-Ah-!", Todomatsu screams loudly and he start to seeing stars. Karamatsu hitting him right on his prostate and the pace is really driving him crazy. His neglected dick starting to ooze many precums and twitching.

Karamatsu leans forward and his hands going to Todomatsu's nipples, circling it and flicking it, before pinching and pulling it lightly.

"A-Ah! N-No! N-No more! I-I want to cum, p-please! Ah!", Todomatsu shivering and moans even louder as his tears flowing down more and more.

"I'm also close too, baby. Do you want my knot, Omega?", Karamatsu said and he suck on the juncture of Todomatsu's neck and shoulder before biting it, leaving hickeys and bite marks everywhere.

"Y-Yes! P-Please! Hh-hah! G-Give me! Give me your knot! Ah! Ah", Todomatsu moans loudly and he clench even tighter around Karamatsu, like trying so hard to milk his Alpha.

"Such a good boy, take it then.", Karamatsu hand going down and start to pump his little brother's dick in a same pace as his thrust.

"Ah-! A-Ah! Alpha!", Todomatsu starting to shake violently and he finally screams out his Alpha name as he reach his orgasm, spurting out white ropes of his cum to the bed as his vision whiten for a while.

Karamatsy groans as he feel the walls clenching and unclenching around him, and he finally can feel his knot starting to form and he start to pound even harder, trying to push his knot into the tight ring.

Todomatsu whimpers in pain as he felt the knot starting to force his entrance to widen up more and he grab his Alpha's hand, trying to make him notice his discomfort.

Karamatsu notice it and he entertwine his fingers with Todomatsu as he groans and huffing.

"Please bear with it for a while, Todomatsu.. Hhah.."

He finally force his hips forward and plant his knot inside, followed by Todomatsu's loud whimpers. He start to grind his hips as he tried to reach his orgasm.

Karamatsu leans forward and catch his Omega's lips with him to distract him from the pain.

After a few grinds, Karamatsu's hips finally stutter as he shoot his sperm deep inside Todomatsu. Todomatsu who feel it finally moans inbetween the kisses because he felt so _full_.

"You take it so good, baby.. I'm proud of you", Karamatsu groans as he peppers his Omega's face with kisses, and doesn't forget to compliment his lover too.

"Ngh.. Hhah.. I-It's so good..", Todomatsu eyes are still blue and it's flickering between blue and black constantly, signaling that his usual Todomatsu is going to be conscious.

Karamatsu leave a final smooch before he blinks his red eyes away and he moves, pulling Todomatsu with him into a spoon.

Todomatsu settles in his Alpha's arms before his breath finally calming down, and then his eyes are finally black again. Realization finally hit him.

"Nii-san!", Todomatsu screams.

Karamatsu is almost fall into the slumber but then flinched when he hear his little brother scream. "Y-Yes?", he answer panickly.

"You're not wearing a condom! What if i get pregnant?!", Todomatsu screech and he kick his brother leg. That movement causing Karamatsu's knot to rub against his prostate and he whimpers again.

"B-But.. You asked me to fill you with my pups..", Karamatsu ears are flopping down and he whimpers like a lost puppy.

"Tch! You must be responsible for this. And! Why are you coming so much? Ngh-", Todomatsu flinch when he feels another shoot of his Alpha's cum inside him.

Karamatsu laughs and hugs his little brother even tighter, "Oops? No let's sleep because your heat is going to hit in a few minutes.", he nuzzles against his lover's shoulder and sniffing deep his Omega's sweet scent.

"... Stupid..", Todomatsu huffs before he finally close his eyes to rest before his next wave hitting him.

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Jyushimatsu and Ichimatsu both going upstair to join his older brother.

Osomatsu startled when the door opened and revealing his half-asleep brothers. Choromatsu suggles more into his chest because of the slight noisy sound.

"What happen?", Osomatsu looks at his little brothers in confusion.

"Karamatsunii-san is taking care of Todomatsu. He got an unpredictable heat and we're kicked out before Jyushimatsu fully awakes", Ichimatsu yawns as he drags his sleeping Alpha and throw him to the bed before nestled in his Alpha's arms.

"Ahh.. It's gonna be another long week for you, then. Let's just play pachinko all days.", he grins and rubs his nose.

"Whatever. I want to sleep more. Night", Ichimatsu said lazily before he join Jyushimatsu into dreamland.

"Hheeee~? Then i'm taking your money to play later", Osomatsu huffs before he snuggle again with his sleeping Omega.

"Touch my wallet and i'll let Jyushi bite your butt, Osomatsunii-san.", Ichimatsu threat deadly.

Osomatsu shivers from the sentence alone. No need to look at his weird little brother's face to know that it's a scary threat.

"Ah, yabai yabai. Omegas in our house is really scary", he mumbles and then yawns as he finally close his eyes again.

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 ** _FIN._**


End file.
